1. Field of the Invention
The present invention relates to a method of manufacturing stay rings for water turbines or pump turbines and, more particularly, to a method of manufacturing stay rings suitable for use in water turbines adapted to be used under a large water head or fall.
2. Description of the Prior Arts
The stay ring incorporated in water turbines and pump turbines usually has an upper annular disc and a lower annular discs axially spaced from each other and a plurality of circumferentially equi-distantly spaced stay vanes each of which extending between the upper and lower annular discs.
According to the conventional method of manufacturing such a type of stay ring, the upper and the lower annular discs and the stay vanes are fabricated separately. Then, after correctly locating the stay vanes between the upper and the lower annular discs, welding is effected along the peripheries of the upper and lower ends of the stay vanes, so as to rigidly connect the vanes to the upper and lower annular discs.
However, this conventional method is extremely inefficient and cannot suitably be applied to the manufacture of stay rings of water turbines intended for use under a large water head or fall. This is because the distance between the upper and the lower annular discs is too small, in such a type of stay ring. In fact, in some cases, the distance between two annular discs at the inner peripheries of these rings is as small as 28 cm, for example. Thus, it is extremely difficult to effect a satisfactory welding by inserting the welding instruments into the limited space between the upper and the lower annular discs. Therefore, the desired quality of the welded parts can hardly be obtained and, moreover, it is often experienced that the welding itself cannot be carried out.